A (non-limiting) example of a cable tensioning system with which the override release mechanism of the invention can be used is a known electrically actuated cable brake mechanism which comprises a cable tensioning drive nut threaded onto a lead screw. A motor rotates the lead screw on instructions from an electronic control unit (ECU) to cause tensioning of a brake cable when it is desired to actuate the brake. The reaction force to cable movement is established through a flexible outer conduit for the cable.
Other malfunctions that might prevent the intended brake release would be a loss of power from the vehicle battery, an electrical fault in the ECU, a fault in the wiring connecting the ECU to the motor driving the lead screw, failure in the motor itself, damage to the bearings mounting the lead screw, or damage to one or more of the gears between the driving motor and the lead screw. If any of the above faults takes place while the brakes are engaged, then in the absence of an override release mechanism, the vehicle is immobilized and cannot even be towed to a garage for repair.
It has been proposed to provide a flexible drive shaft from a manual control wheel to a shaft of the electric motor driving the electrically activated cable brake mechanism, so that in the event of motor failure, the lead screw can be rotated manually through the drive shaft so as to release the tension in the cable brake, permitting the vehicle to be towed to a repair garage. That is, however, only a partial solution to the problem because if the drive nut is cross-threaded on the lead screw, or if the brake malfunction is due to a fault in the gear box or a bearing fault and the electrically actuated cable brake mechanism becomes seized solid in the brake-applied condition, then no manual hand wheel will permit the lead screw to be rotated so as to release the cable tension.
It is an object of this invention to provide an override release mechanism which can rapidly and reliably release the tension in the cable, irrespective of whether the malfunction in the electrically actuated cable tensioning mechanism is an electrical malfunction that results in a total seizure of the cable tensioning mechanism.